In the exploration and production of oil and gas, centralizers are used to keep casing, tubing, and/or sucker rods centered in a borehole for a number of reasons. For example, centralizers reduce friction while running in the hole or moving up and down, they protect the pipe or coupling, they insure a proper cement job, and, as in the case of some plastic centralizers, they act as electrical isolators.
In some cases, centralizer-like devices are run as “clamps” or “protectors” with a primary purpose to secure an electrical or hydraulic umbilical against a tubular, such as with ESP cables, SCSSV control lines, chemical injection lines, PDG-wires, and the like. In such applications, electrical insulation of the tubing from the casing is not important. Such systems are usually fabricated from metal, though economics (not functionality) may demand that plastic or insulating materials be used.
As systems are introduced that require an EM transmission line to be constructed of concentric tubular, it is important to keep the tubing from directly shorting out against the casing string. It is also desirable to keep the inner tubular more or less concentric with the casing string over the length of the well to minimize signal attenuation.
Some centralizers are fabricated as one piece and are slipped over one end of a drill pipe. A disadvantage of such centralizers is that they normally require additional components to anchor them in place on a drill pipe because, if they are left free to float so that they can slide until they hit an upset or a coupling, their linear placement is not controlled and then, even if they are placed on every 30 foot joint, they may end up being as much as almost two joints (i.e., almost 60 feet) apart, and thus be less effective.
Alternatively, centralizers may be designed so that they are hinged and pinned (or bolted) together, so that they must be assembled on a rig floor, and can be placed anywhere along a drill pipe or even over a threaded connection. A disadvantage of such centralizers is that they generally require additional hardware as part of the assembly and for securing it in place on a drill pipe. Such assembly can causes delays, especially if the loose pieces are dropped, because then work must stop to search for the lost piece or get a new piece. If proper provisions are not made and adhered to, pieces may fall into the wellbore and cause equipment failure. Having to take extra precautions to prevent small pieces of hardware from falling into the well bore, such as, for example, covering up around the pipe with tarp or plastic covers create a major tripping hazard. This hazardous condition is quickly worsened as more people and tools are involved in the operation. Another disadvantage of having to assemble a centralizer is that assembly generally requires at least two people, one person to hold the assembly while another person assembles the centralizer. Yet another disadvantage is the cost of having the extra components that secure the centralizer in place.
There is thus a need for a centralizer that can be easily, quickly, and safely installed and removed by a single person so that rig idle time is minimized and other personnel are freed up to perform other functions on a rig while installing or removing pipe from a well. Such systems and methods should, among other things, also provide tubing-to-casing electrical isolation and stand-off, and allow for fluids to pass relatively freely along the annulus to assist in running and pulling the tubing and to provide for circulation operations.